IJN Submarine RO-50:
Tabular Record of
© 2001-2017 Bob Hackett & Sander Kingsepp
18 February 1943:
Tamano. Laid down at Mitsui Zosensho as a 960-ton type K6 submarine.
27 November 1943:
Launched and numbered RO-50.
5 June 1944:
LtCdr (Cdr, posthumously) Kimura Masao (63)(former CO
of I-159) is appointed the Chief Equipping Officer (CEO).
31 July 1944:
Completed, commissioned and attached to Maizuru
Naval District. Assigned to SubRon 11 for working-up. LtCdr Kimura Masao is
the Commanding Officer.
20 October 1944: American Operation "KING TWO" - The Invasion of Leyte,
Admiral (later Fleet Admiral) William F. Halsey's (USNA '04)
Third Fleet of 738 ships including 18 aircraft carriers, six battleships, 17
cruisers, 64 destroyers and over 600 support ships land the Army's X Corps (24th
Infantry and 1st Cavalry Divisions) and the XXIV Corps (7th, 77th and 96th
Infantry Divisions) that begin the campaign to retake Leyte.
23 October 1944: Operation "TA" - The Reinforcement of Leyte:
Admiral Mikawa Gunichi (38)(former CO of KIRISHIMA), CINC, Southwest Area Fleet,
commences Operation TA to provide reinforcements, supplies and munitions to the
IJA's forces engaging the Americans on Leyte. Between 23 October and 11 December
1944, nine major reinforcement convoys attempt the 600-mile passage from Manila
to Ormoc Bay, Leyte.
5 November 1944:
Reassigned to SubDiv 34 in Vice Admiral Miwa
Shigeyoshi's (39)(former CO of CL KINU) Sixth Fleet (Submarines).
19 November 1944:
Departs Kure on her first war patrol for an area E
22 November 1944:
En route, RO-50 is attacked by a IJNAF floatplane
that drops two depth-charges. The submarine dives to 130 feet and escapes
25 November 1944:
150 nms NE of Lamon Bay, Luzon, Philippines.
RO-50's Type 13 radar detects a plane, presumably launched from a carrier.
LtCdr Kimura starts a chase. Five hours later his sonarman detects screw noises.
Soon thereafter, three carriers and eights destroyers in a ring formation are
sighted. RO-50 continues to approach and breaks through the escort's screen.
Suddenly, Kimura sights a WASP-class carrier dead ahead, 875 yards away! He
fires a four-torpedo salvo at the carrier and submerges to 263 feet. A massive
explosion follows. Five minutes later the sonar operator reports breaking-up
noises that continue for the next two minutes. 
Later, LtCdr Kimura reports sinking an American escort carrier and a
destroyer, but his claims are not substantiated postwar.
27 December 1944:
Returns to Kure.
9 January 1945: American Operation "MIKE ONE" - The Invasion of Luzon:
Vice Admiral (later Admiral) Thomas C. Kinkaid's (USNA '08) Task Force 77
lands almost 175,000 men of LtGen (later Gen) Walter Krueger's Sixth Army at
Lingayen Gulf, Philippines under the cover of Vice Admiral (later Admiral) Jesse
B. Oldendorf's (USNA '09) TG 77.2 bombardment force and aircraft of Rear Admiral
(later Vice Admiral) Calvin T. Durgin's (USNA ’16) TG 77.4. The Sixth Army
begins a campaign to retake Luzon from General Yamashita Tomoyuki's 14th Area
23 January 1945:
Departs Kure for the area E of Luzon on her second
war patrol. Vice Admiral Miwa and his staff arrive to see her off.
1 February 1945:
Leyte, Philippines. LtCdr Kimura sights a target and
gives chase, but it turns out to be a hospital ship.
3 February 1945:
E of Luzon. RO-50 is briefly chased by an American
anti-submarine vessels. RO-50 escapes, but is damaged. 
4 February 1945:
Vice Admiral Miwa orders RO-50 to stand by to rescue
naval pilots from Batulinao, Philippines.
10 February 1945:
300 nms ESE of Surigao, Leyte, Philippines. At
0805, LtCdr Kimura fires a four-torpedo salvo at an enemy reinforcement convoy
sailing in a single column at 08-01N, 136-37E. Landing Ship Tank (LST)-577 is
proceeding from Hollandia, New Guinea to Leyte in the convoy. At about 0810,
LST-577 in a group a few thousand yards starboard off LtCdr Louis E. Schmidt's
USS ISHERWOOD (DD-520), is hit by a torpedo. About 1/3 of LST-577 is blown clean
off including the entire bridge. Another LST prepares to tow her. Both
transport groups and their escorts depart the area. ISHERWOOD commences a box
After sunset, RO-50 surfaces. At 2110, ISHERWOOD makes radar contact on a
surfaced sub at 14,000 yards. The destroyer goes to General Quarters and rings
up turns for 25 knots. At 1500 yards, first the starboard, then the port,
search light is turned on, but neither can bear. LtCdr Kimura finds an enemy
destroyer illuminating RO-50 from her port quarter and crash-dives to 395 feet.
ISHERWOOD picks up RO-50 on her sound gear and drops a full pattern at
shallow setting. The depth-charges rupture RO-50's diving tank valves and
shatter the lenses in both periscopes. All of RO-50's torpedo tubes start to
leak. ISHERWOOD drops two more full patterns and several persons report smelling
oil including the Captain. After a third run, the destroyer is unable to regain
After escaping, RO-50 surfaces. A 40-lb depth-charge fragment is
recovered from her afterdeck. LtCdr Kimura reports sinking an American cargo
11 February 1945:
ISHERWOOD scuttles LST-577 E of Mindanao at 08-05N,
14 February 1945:
LtCdr Kimura sends a situation report to Sixth
Fleet HQ. He receives permission to return to base after reconnoitering the
Nansei Shoto area.
19 February 1945:
S of Kyushu. Kure-bound RO-50 is attacked by an
IJNAF plane that drops three depth-charges.
20 February 1945:
Returns to Kure. Later, she is transferred to
2 April 1945:
Lt Imai Umeichi (67)(former torpedo officer of I-8) is
appointed the CO.
20 April 1945:
Departs Maizuru on her third war patrol and proceeds
through the Bungo Suido Channel for the Kita-Daito-Jima area.
28 April 1945:
Off Kita-Daito-Jima. RO-50's sonar operator detects
the screw noises of an enemy task force but the distance is too great for an
4 May 1945:
Returns to Kure, then proceeds to Maizuru.
29 May 1945:
Departs Maizuru for East China Sea on her fourth war
6 June 1945:
Arrives at her assigned area E of Taiwan. She is next
redirected to an area between Ulithi and Okinawa.
3 July 1945:
Returns to Maizuru.
15 August 1945:
Emperor Hirohito (Showa) broadcasts an Imperial
Rescript calling for an end to the hostilities. That same day, SubDiv 34 is
disbanded. RO-50 is reassigned to SubDiv 15.
RO-50, one of the few remaining operational IJN
submarines, is surrendered.
30 November 1945:
Removed from the Navy List.
1 April 1946: Operation "ROAD'S END":
RO-50 is stripped of all usable
equipment and material. She is scuttled 16 nms off Kinai Island on bearing 090
from Goto Island.
 Author/historian Kimata Jiro suggests this was Sherman’s
TG 38.3. Author Ivan Musicant's " Battleship at War: The Epic Story of USS
WASHINGTON" mentions the attack. Lookouts on WASHINGTON sighted two torpedo
tracks passing ahead, one of which evidently had faulty steering. It appears
what Kimura heard was prematures or end-of-run explosions.
 Possibly USS TISDALE (DE-33). On 3 Feb '45, while en route back to
Manus on a round-trip convoy escort voyage, TISDALE attacked a sonar contact.
Special thanks go to Dr. Higuchi Tatsuhiro of Japan and to Brad Isherwood
for info on the events of 10/11 February 1945.
– Bob Hackett and Sander Kingsepp.
Back to Submarine